Field of the Invention
The present invention relates to a method of forming a cut groove in a workpiece such as a wafer or the like along a projected dicing line set on the workpiece.
Description of the Related Art
In the process for fabricating semiconductor devices, it has been customary to define a plurality of regions on the surface of a semiconductor wafer, such as a silicon wafer, a gallium arsenide wafer, or the like which is in the shape of a substantially circular plate, with projected dicing lines referred to as streets formed in a grid pattern, and to form devices such as ICs, LSI circuits, or the like in the respective regions. After the semiconductor wafer has been ground on its reverse side to a predetermined thickness by a grinding apparatus, the semiconductor wafer is divided by a cutting apparatus or a laser machining apparatus into individual devices that will widely be used in various electric devices including cellular phones, personal computers, etc.
A cutting apparatus which is generally called a dicing saw is used as the cutting apparatus referred to above. The cutting apparatus includes a cutting blade having a cutting edge which is made of a superabrasive such as diamond, CBN, or the like bound together by metal or resin and has a thickness in the range from 20 μm to 30 μm. While the cutting blade is rotating at a high speed of about 30000 rpm or the like, it incises the semiconductor wafer to cut the same.
Each of the semiconductor devices formed on the surface of the semiconductor wafer includes metal interconnects deposited in several layers for transmitting signals. The layered metal interconnects are insulated from each other by interlayer insulating films that are mainly made of SiO2. In recent years, structural miniaturization results in smaller distances between interconnects, increasing the electric capacitance between adjacent interconnects. This causes signal delays, making manifest the problem of increased electric power consumption.
In order to reduce parasitic capacitances between layers, it has heretofore been the practice to mainly employ SiO2 insulating films as interlayer insulating films at the time of forming devices (circuits). However, low-dielectric-constant insulating films (low-k films) whose dielectric constants are lower than SiO2 insulating films have recently started to find use. Such low-dielectric-constant insulating films include materials having dielectric constants (e.g., dielectric constant k=about 2.5 through 3.6) lower than that (k=4.1) of SiO2 insulating films, for example, inorganic films of SiOC, SiLK, etc., organic films as polymer films of polyimide, parylene, polytetrafluoroethylene, etc., and porous silica films of methyl-contained polysiloxane, etc.
When a laminated body including low-dielectric-constant insulating films is cut along projected dicing lines by a cutting blade, the laminated body tends to flake as the low-dielectric-constant insulating films are very brittle like mica. Heretofore, there has been known a processing method based on a combination of laser dicing and mechanical dicing as a method of well dividing a semiconductor wafer of the above type into individual chips (see, for example, Japanese Patent Laid-Open No. 2005-150523).
According to the above wafer processing method, a laser beam is applied to the surface of the semiconductor wafer to form laser-processed grooves dividing the laminated body which includes a low-k film and a functional film, and then a substrate exposed on the bottom surfaces of the laser-processed grooves is cut by a cutting blade, dividing the semiconductor wafer into individual device chips. The wafer processing method makes it possible to divide the semiconductor wafer into individual device chips while preventing the low-k film from flaking off. However, the wafer processing method is problematic in that because it is necessary to use a laser processing apparatus in addition to a cutting apparatus, the cost of the apparatus used is high.
Methods of cutting a low-k film without flaking it off by way of mechanical dicing without the use of a laser processing apparatus have been researched and developed from day to day. A very shallow-cutting processing method of removing a low-k film with a cutting blade which has a cross-sectionally U-shaped or V-shaped tip end is described in Japanese Patent Laid-Open No. 2015-18965.